Multilayer insulated wire and transformer using the same

ABSTRACT

A multilayer insulated wire has two or more extrusion-coating insulating layers provided on a conductor directly or via some other layer, or provided on the outside of a multicore wire composed of conductor cores or insulated cores that are collected together, wherein at least one of the insulating layers is made of a mixture prepared by mixing 100 parts by weight of a polyethersulfone resin and 10 to 100 parts by weight of an inorganic filler. A transformer utilizes the multilayer insulated wire. The multilayer insulated wire can realize such high heat resistance as heat resistance F class (155° C.), which satisfies IEC 950 standards, or higher heat resistance, in transformers; and can exhibit excellent electrical properties even at high frequencies. Further, when the transformer is used at high frequencies, the electric properties are not lowered, and influence by the generation of heat can be prevented.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP98/04491 which has an Internationalfiling date of Oct. 5, 1998, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a multilayer insulated wire having twoor more insulating layers, and a transformer wherein the same isutilized. More specifically, the present invention relates to amultilayer insulated wire having excellent heat resistance andhigh-frequency properties and useful as a lead wire and a winding usedin a transformer to be incorporated in electronic/electrical equipmentand the like. The present invention also relates to a transformer thatutilizes the multilayer insulated wire.

BACKGROUND ART

The structures of transformers are stipulated, for example, in IECstandards (International Electrotechnical Communication Standards), Pub.950. These standards stipulate, for example, that, in the windings, theenamel film coating the conductor is not recognized as an insulatinglayer; an insulator having a stipulated thickness, or a thickerinsulator, is to be inserted between the primary winding and thesecondary winding; or, a three-layer insulator, wherein, out of thethree layers, two arbitrary layers pass the test of the stipulatedwithstand voltage (in the case of an operating voltage of 1,000 V, theyshould withstand for 1 min or more with 3,000 V being applied), is to beinserted between the primary winding and the secondary winding; and astipulated creeping distance is to be taken between the primary windingand the secondary winding.

Accordingly, in the currently predominant transformer, wherein anenameled wire is used, the structure shown in FIG. 2 in cross section,for example, is employed. That is, the structure is such that insulatingbarriers (2), for securing a creeping distance, are arranged on oppositeends of the circumferential surface of a bobbin (1); a primary winding(3) is wound between the insulating barriers; an insulating tape (4) iswound thereon at least three times; and then insulating barriers (2),for securing a creeping distance, are arranged on opposite ends of thecircumferential surface, and a secondary winding (5) is wound betweenthem.

Additionally, in recent years, in place of the transformer having thestructure shown in FIG. 2, a transformer having the structure shown inFIG. 1 in cross section, for example, has begun to appear. The featureof this transformer hasan overal is that it is small zize ,by omittingthe insulating barriers (2) and the insulating tape (4), by using aninsulated wire having at least three insulating layers as the primarywinding (3) and/or the secondary wire (5). In the example shown in FIG.1, the primary winding (3) has three insulating layers (3 b, 3 c, and 3d) on the outer circumferential surface of a conductor (3 a). Thisstructure brings about an advantage that the number of steps ofoperations for winding the insulating barrier (2) and the insulatingtape (4) can be reduced/omitted.

Known of such a three-layer insulated wire include are one in which afirst insulating layer is formed by winding an insulating tape aroundthe outer circumference of a conductor, and then another insulating tapeis wound around thereon, to form a second insulating layer, and then athird insulating layer is formed thereon; and one in which, instead ofthe insulating tapes, a fluororesin is successively extruded onto theouter circumference of a conductor, to form three insulating layers inall (JU-A-3-56112(“JU-A” means unexamined published Japanese utilitymodel application)).

However, the insulation by the above insulating tape winding cannotavoid the winding operation, and therefore it has the problem that theproductivity is tremendously low, to increase the production cost.Further, although the above insulation with a fluororesin is excellentin heat resistance and high-frequency properties, the cost of the resinis high, and further, when the conductor is pulled at a high shear rate,the state of the external appearance characteristically deteriorates.Therefore it is difficult to increase the production speed, leading tothe fault that the cost of the electric wire with the fluororesin ismade very high, similar to the insulating tape winding, and theproduction cost of the transformer is increased as a result. To solvesuch problems, the inventors of the present invention proposed, forexample, an insulated wire in which a polyester resin that is modifiedso that crystallization may be prevented from occurring and reduction ofthe molecular weight may be suppressed, is extruded onto the outercircumference of a conductor, to form a first and a second insulatinglayer, and then a polyamide resin is extruded as a third insulatinglayer for the covering (JP-A-6-22334 (“JP-A” means unexamined publishedJapanese patent application (U.S. Pat. No. -A-5,152)).

However, it cannot be said that such a multilayer extrusion-coatinginsulated wire satisfactorily meets the demand for improvement in theperformance of transformers in the future, which will become more andmore strict.

First, as electrical/electronic equipments have been made small-sized inrecent years, the influence of heat generation on a transformer becomesremarkable therefore, even in the case of the above three-layerextrusion coating insulated wire, higher heat resistance is demanded.Further, the frequency used in circuits of transformers are into highfrequencies, and therefore improvements in electrical properties at highfrequencies are demanded.

To meet such demands, the inventors of the present invention proposed,as a multilayer insulated wire improved in heat resistance, an electricwire covered with an inner layer of a polyethersulfone and the outermostlayer of a polyamide (JP-A-10-13442).

An object of the present invention is to provide a multilayer insulatedwire that solves the above problems involved in conventional multilayerinsulated wires, that realizes such high heat resistance as heatresistance F class (155° C.), which satisfies IEC 950 standards, or;

higher heat resistance, in transformers; and that can exhibit excellentelectrical properties even at high frequencies.

Further, another object of the present invention is to provide atransformer wherein, when it is used at high frequencies, the electricproperties are not lowered, and influence by the generation of heat isprevented.

Other and further objects, features, and advantages of the inventionwill appear more fully from the following description, taken inconnection with the accompanying drawings.

DISCLOSURE OF INVENTION

In view of the above objects, the inventors of the present invention,having investigated intensively, have found that, when at least onelayer out of two or more extrusion-coating insulating layers is formedby using a mixture of 100 parts by weight of a polyethersulfone resin asa favorably extrudable heat-resistant resin with 10 to 100 parts byweight of an inorganic filler, the heat resistance is further improved,the electric properties at high frequencies are improved, and , further,the heat shock resistance (crack prevention) and the solvent resistanceof the coating insulating layer are improved. The present invention iscompleted based on the above findings.

That is, according to the present invention there is provided:

(1) A multilayer insulated wire having two or more extrusion-coatinginsulating layers provided on a conductor directly or via some otherlayer, or provided on the outside of a multicore wire composed ofconductor cores or insulated cores that are collected together, whereinat least one of the insulating layers is made of a mixture prepared bymixing 100 parts by weight of a polyethersulfone resin and 10 to 100parts by weight of an inorganic filler;

(2) A multilayer insulated wire having two or more extrusion-coatinginsulating layers provided on a conductor directly or via some otherlayer, or provided on the outside of a multicore wire composed ofconductor cores or insulated cores that are collected together, whereinat least one of the insulating layers is made of a mixture prepared bymixing 100 parts by weight of a polyethersulfone resin and 20 to 70parts by weight of an inorganic filler;

(3) The multilayer insulated wire as stated in the above (1) or (2),wherein the insulating layer made of the mixture is formed at least asthe outermost layer.

(4) The multilayer insulated wire as stated in the above (1), (2), or(3), wherein the proportion of the inorganic filler in the mixture isincreased in an outer layer than an inner layer, successively.

(5) The multilayer insulated wire as stated in any one of the above (1),(2), (3), or (4), wherein the inorganic filler comprises at least oneselected from among titanium oxide and silica.

(6) The multilayer insulated wire as stated in any one of the above (1),(2), (3), (4), or (5), wherein the inorganic filler has an averageparticle diameter of 0.1 to 5 μm.

(7) A multilayer insulated wire, comprising the multilayer insulatedwire stated in any one of the above (1), (2), (3), (4), (5), or (6)whose surface is coated with a paraffin and/or a wax; and

(8) A transformer, wherein the multilayer insulated wire stated in anyone of the above (1), (2), (3), (4), (5), (6), or (7) is utilized.

Meanwhile, the outermost layer in the present invention refers to thelayer situated farthest from the conductor out of the extrusion-coatinginsulating layers.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating an example of thetransformer having a structure in which three-layer insulated wires areused as windings.

FIG. 2 is a cross-sectional view illustrating an example of thetransformer having a conventional structure.

FIG. 3 is a schematic diagram showing a method of measuring staticfriction coefficients.

BEST MODE FOR CARRYING OUT THE INVENTION

The insulated wire of the present invention is characterized in that ithas two or more, preferably three extrusion-coating insulating layers,and at least one layer thereof is made of a mixture of a given resinwith an inorganic filler.

The resin in the mixture is a polyethersulfone resin, and the use ofthis polyethersulfone resin improves the heat resistance, theextrudability, and the flexibility in the function of the electric wire.

Herein, as the polyethersulfone resin for use in the present invention,can be mentioned those having the structure of the following formula(1):

wherein R₁ represents a single bond or —R₂—O—, in which R₂, which mayhave a substituent (e.g. an alkyl group), represents a phenylene groupor a biphenylylene group, and n is a positive integer large enough togive the polymer.

The method of producing this resin is known per se, and as an example, amanufacturing method in which a dichlorodiphenyl sulfone, bisphenol S,and potassium carbonate are reacted in a high-boiling solvent, can bementioned. As commercially available resins, for example, SumikaexcelPES (trade name, manufactured by Sumitomo Chemical Co., Ltd.), Radel Aand Radel R (trade names, manufactured by Amoco) can be mentioned.

Further, the larger the molecular weight of the resin is, the morepreferable it is and the more improved the flexibility in the functionof the electric wire is. However, if the molecular weight of the resinis too large, it is difficult to extrude the resin into a thin film. Inthe present invention, the polyethersulfone resin has a reducedviscosity that is directly proportional to the molecular weight (aviscosity of a dimethylformamide solution of a polyethersulfone resin (1g of a polyethersulfone resin (PES) in 100 ml of dimethylformamide) in athermostat at 25° C., to be measured using a Ubbelohde's viscometer), ofpreferably 0.36 or more, and particularly preferably in the range of0.41 to 0.48.

Particularly, when the amount of an inorganic filler to be used islarge, it is preferable to use a polyethersulfone resin whose reducedviscosity is large, in view of flexibility of the resultant insultedwire.

In the insulated wire of the present invention, an insulating layerother than the insulating layer which is made of the mixture of apolyethersulfone resin and an inorganic filler, may be made of only aresin without any inorganic filler, and such a resin is most preferablya polyethersulfone resin, in view of heat-resistance and extrudability.

Alternatively, in place of a polyethersulfone resin, a polyetherimideresin can be used to make an insulating layer, although thepolyetherimide resin is inferior to the polyethersulfone resin in viewof extrudability into a thin film.

The polyetherimide resin can be synthesized, for example, by solutionpolycondensation of 2,2′-bis [3-(3,4-dicarboxyphenoxy)-phenyl]propanediacid anhydride and 4,4′-diaminodiphenylmethane inortho-dichlorobenzene as a solvent, and as commercially availableresins, for example, ULTEM (trade name, manufactured by GE PlasticsLtd.) can be used.

Next, as the inorganic filler that can be used in the present invention,can be mentioned titanium oxide, silica, alumina, zirconium oxide,barium sulfate, calcium carbonate, clay, talc, and the like. Among theabove, titanium oxide and silica are particularly preferable, becausethey are good in dispersibility in a resin, particles of them hardlyaggregate, and they hardly cause voids in an insulating layer, as aresult, the external appearance of the resulting insulating wire is goodand abnormality of electrical properties hardly occurs. Preferably theinorganic filler has an average particle diameter of 0.01 to 5 μm, andmore preferably 0.1 to 3 μm. If the particle diameter is too large, theexternal appearance of the electric wire is sometimes deterioratedbecause of such problems as the inclusion of voids and a decrease in thesmoothness of the surface. Further, an inorganic filler high in waterabsorption property lowers the electric properties sometimes, andtherefore an inorganic filler low in water absorption property ispreferable. Herein, “low in water absorption property” means that thewater absorption at room temperature (25° C.) and a relative humidity of60% is 0.5% or less.

The commercially available inorganic filler that can be used in thepresent invention includes, for example, as titanium oxide, FR-88 (tradename;

manufactured by FURUKAWA CO., LTD.; average particle diameter: 0.19 μm),FR-41 (trade name; manufactured by FURUKAWA CO., LTD.; average particlediameter: 0.21 μm), and RLX-A (trade name; manufactured by FURUKAWA CO.,LTD.;

average particle diameter: 3 to 4 μm); as silica, UF-007 (trade name;manufactured by Tatsumori, LTD.; average particle diameter: 5 μm) and 5X(trade name; manufactured by Tatsumori, LTD.; average particle diameter:1.5 μm); as alumina, RA-30 (trade name; manufactured by IwataniInternational Corporation; average particle diameter: 0.1 em); and ascalcium carbonate, Vigot-15 (trade name; manufactured by SHIRAISHI KOGYOKAISHA, LTD.; average particle diameter: 0.15 μm) and Softon (tradename; manufactured by BIHOKU FUNKA KOGYO CO., LTD.; average particlediameter: 3 μm).

The proportion of the inorganic filler in the above mixture is 10 to 100parts by weight, to 100 parts by weight of the above resin. If theproportion is less than 10 parts by weight, the desired highheat-resistance and high-frequency properties cannot be obtained,further the heat shock resistance becomes bad, cracks reaching theconductor cannot be prevented from occurring, and in addition thesolvent resistance is poor. On the other hand, if the proportion is over100 parts by weight, the dispersion stability of the inorganic fillerand the flexibility in the function of the electric wire areconspicuously lowered, and as a result the electric properties(breakdown voltage and withstand voltage) are deteriorated. The heatshock resistance in the present invention refers to the property againstheat shock due to winding stress (simulating coiling). In view of thebalance among the heat resistance, the high-frequency properties, theheat shock resistance, the solvent resistance, and other desiredelectric properties, preferably the proportion of the inorganic filleris 20 to 70 parts by weight, and more preferably 25 to 50 parts byweight, to 100 parts by weight of the above resin.

The above resin mixture for use in the present invention can be preparedby melting and mixing by using a conventional mixer, such as atwin-screw extruder, a kneader, and a co-kneader. There is no particularrestriction on the mixing temperature and the like. However, it ispreferable to dry out of the resin and the inorganic filler well , sothat absorber the water absorption may be 0.1% or less, respectively.

To the above mixture can be added additives, processing aids, andcoloring agents, each of which are usually used, in such amounts thatthey do not impair the action and effects to be attained according tothe present invention, to make the resin composition for extruding andcoating.

In the present invention, at least one layer out of the two or moreinsulating layers of the insulated wire is an insulating layer made ofthe above mixture. The position of the insulating layer made of theabove mixture is not particularly limited, and that layer may be theoutermost layer or an layer other than the outermost layer.) When aninsulated wire is applied with a voltage higher than a partial dischargeinception voltage by any cause, surface breakage due to corona may beginfrom the vicinity of parts where electric wires contact to each other,which breakage occurs more intensively under high-voltage andhigh-frequency, making break of wire easily proceed, thereby causing thedeterioration of the electric properties. Therefore, in order to preventthis phenomenon, it is preferable that the layer made of the abovemixture of a polyethersulfone resin and an inorganic filler is providedat least the outermost layer (and optionally another insulating layer)in the insulated wire of the present invention. In this case, in view ofthe improvement, for example, in the heat resistance and the heat shockresistance, all the layers can be made of the above mixture, but in somecases, the electric properties (breakdown voltage and withstand voltage)are lowered a little. Therefore, preferably one layer or several layersout of all the layers are made of the above mixture, or the proportionof the inorganic filler is greater in an outer layer than in an innerlayer. In this case, if only the outermost layer is made of the abovemixture, the heat resistance, the high-frequency V-t property, thesolvent resistance, and the heat shock resistance can be greatlyimproved, but one wherein the proportion of the inorganic filler isincreased in the more outer layer is more preferable because theadhesion between the layers is improved.

Preferably, the overall thickness of the extrusion-coating insulatinglayers thus formed is controlled within the range of 60 to 180 μm.Particularly preferable, the overall thickness of the extrusion-coatinginsulating layers is in the range of 70 to 150 μm. Preferably, thethickness of each of the insulating layers is controlled within therange of 20 to 60 μm.

The multilayer insulated wire of the present invention may be providedwith a covering layer having a specific function as an outermost layerof the electric wire, on the outside of the above two or moreextrusion-coating insulating layers. For the insulated wire of thepresent invention, if necessary, a paraffin, a wax (e.g. a fatty acidand a wax), or the like can be used, as a surface-treating agent. Therefrigerating machine oil used for enameled windings has poor lubricityand is liable to make shavings in the coiling operation, but thisproblem can be solved by applying a paraffin or a wax in the usualmanner.

As the conductor for use in the present invention, a bare conductor, aninsulated conductor having an enamel film or a thin insulating layercoated on a bare conductor, a multicore stranded wire composed ofintertwined conductor cores, or a multicore stranded wire composed ofintertwined insulated-wires that each have an enamel film or a thininsulating layer coated, can be used. The number of the intertwinedwires of the multicore stranded wire (a so-called litz wire) can bechosen arbitrarily depending on the desired application. Alternatively,when the number of wires of a multicore wire is large, for example, in a19- or 37-element wire, the multicore wire (elemental wire) may be in aform of a stranded wire or a non-stranded wire. In the non-strandedwire, for example, multiple conductors that each may be a bare wire oran insulated wire to form the element wire, may be merely gathered(collected) together to bundle up them in an approximately paralleldirection, or the bundle of them may be twisted in a very large pitch.In each case of these, the cross-section thereof is preferably a circleor an approximate circle.

The multilayer insulated wire of the present invention can be used as awinding for any type of transformer, including those shown in FIG. 1. Ina transformer, generally a primary winding and a secondary winding arewound in a layered manner on a core, but the multilayer insulated wireof the present invention may be applied to a transformer in which aprimary winding and a secondary winding are alternatively wound(JP-A-5-152139). Further, in the transformer of the present invention,the above multilayer insulated wire may be used for both the primarywinding and the secondary winding, and if the insulated wire havingthree-layered extruded insulating layers is used for one of the primaryand the secondary windings, the other may be an enameled wire.Additionally stated, in the case wherein the insulated wire having twoextruded insulating layers is used only for one of the windings and anenameled wire is used for the other, it is required that one layer of aninsulating tape is interposed between the windings and an insulatingbarrier is required to secure a creeping distance.

The multilayer insulated wire of the present invention has suchexcellent actions and effects that it has high enough heat-resistancehigh enough to satisfy the heat resistance F class, it has highsolvent-resistance, cracks due to heat shock are not formed, and,further, electric properties at high frequencies are good. Thetransformer of the present invention wherein the above multilayerinsulated wire is utilized, can meet the requirements forelectrical/electronic equipments that are increasingly made small-sized,because the transformer is excellent in electrical properties withoutbeing lowered in electric properties when a high frequency is used in acircuit, and the transformer is less influenced by generation of heat.

EXAMPLES

The present invention will now be described in more detail withreference to the following examples, but the invention is not limited tothem.

Examples 1 to 9 and Comparative Examples 1 to 3

Three layers of insulating coatings made of resin mixtures having thecompositions shown in Tables 1 and 2 were formed on each of theconductors shown in Tables 1 and 2, and the surface treatments shown inTables 1 and 2 were carried out, to make multilayer insulated wires. InExample 9, the conductor was made of seven-twisted wires each coveredwith a polyamideimide and having a diameter of 0.15 mm and in othercases, the conductor was an annealed copper wire having a diameter of0.4 mmφ. The thickness of each insulating coating was 33 μm and thetotal thickness of all the three layers was 100 μm.

As for the thus obtained multilayer insulated wires, the followingproperties were tested and evaluated. The results are shown in Tables 1and 2.

(1) Solvent Resistance

In accordance with the evaluation of JIS C 3003¹⁹⁸⁴ 14.1 (2) and 15.1,after the insulated wire was immersed in xylene at 60° C. for 30 min,the presence or absence of swelling of the coating was evaluated, andthe pencil hardness was measured.

(2) Dielectric Breakdown Voltage

The dielectric breakdown voltage was measured in accordance with thetwo-twisting method of JIS C 3003⁻¹⁹⁸⁴ 11.(2).

(3) Heat resistance

The heat resistance was evaluated by the following test method, inconformity to Annex U (Insulated wires) of Item 2.9.4.4 and Annex C(Transformers) of Item 1.5.3 of 950-standards of the IEC standards.

Ten turns of the multilayer insulated wire were wound around a mandrelof diameter 6 mm under a load of 118 MPa. They were heated in athermostat for 1 hour at 240° C., and then for 72 hours at 190° C., andthen they were kept in an atmosphere of 25° C. and humidity 95% for 48hours. Immediately thereafter, a withstand voltage of 3 kV was appliedthereto, for 1 min. When there was no electrical short-circuit, it wasconsidered that it passed Class F. (The judgment was made with n=5. Itwas considered that it did not pass the test if it was NG even whenn=1.)

(4) Heat Shock Resistance The heat shock resistance was evaluated inaccordance with IEC 851-6 TEST 9. After winding to the identicaldiameter (1D) was done, it was placed in a thermostat at 240° C. for 30min, and when there was no cracks in the coating, it was judged good.

(5) High-Frequency V-t Property A test specimen was made in accordancewith the two-twisting method of JIS C 3003⁻¹⁹⁸⁴ 11. (2), and the life(min) until the occurrence of short-circuit at an applied voltage of 4kV, a frequency of 100 kHz, and a pulse duration of 10 μs was measured.

(6) Static Friction Coefficients (Coilability) The measuring was donewith an apparatus shown in FIG. 3. In FIG. 3, 7 indicates multilayerinsulated wires, 8 indicates a load plate, 9 indicates a pulley, and 10indicates a load. Letting the mass of the load 10 be F (g) when the loadplate 8 whose mass is W (g) starts to move, the static frictioncoefficient is found from F/W. The smaller the obtained numerical valueis, the better the slipperiness of the surface is and the better thecoilability is.

(7) Water Absorption

The water absorption was measured by a Karl Fischer's type water contentmeasuring apparatus. The hating temperature was 200° C. Parenthetically,the materials used in Examples 1 to 9 and Comparative Examples 1 and 2were dried to have a water absorption of 0.05% or less. The materialused in Comparative Example 3 was dried to have a water absorption of0.2%.

TABLE 1 No. Example 1 Example 2 Example 3 Example 4 Example 5 Example 6First Resin PES*⁰ PES PES PES PES PES layer Inorganic Kind Titanium — —— — — filler oxide*² Proportion*¹ 65 — — — — — Second Resin PES PES PESPES PES PES layer Inorganic Kind Titanium Titanium Titanium — — — filleroxide*² oxide*² oxide*² Proportion*¹ 65 15 15 — — — Third Resin PES PESPES PES PES PES layer Inorganic Kind Titanium Titanium Titanium TitaniumTitanium Silica*⁴ (outer- filler oxide*² oxide*² oxide*² oxide*² oxide*²most Proportion*¹ 65 15 30 30 65 65 layer) Surface-treatmentrefrigerating refrigerating fatty acid fatty acid fatty acid fatty acidmachine oil machine oil wax wax wax wax Solvent resistance (xylene) 5H4H 4H 4H 5H 5H Dielectric breakdown voltage (kV) 16.8 20.9 21.0 22.521.8 17.5 Heat resistance F class passed passed passed passed passedpassed Heat shock resistance good good good good good goodHigh-frequency V-t property (min) 153.7 45.5 50.1 30.2 50.3 17.3 Staticfriction coefficient 0.15 0.17 0.10 0.10 0.10 0.09 (Note) *⁰SumikafcelPES (trade name, manufactured by Sumitomo Chemical Co., Ltd.); reducedviscosity of PES in Examples 1, 5 and 6 was 0.48, and that in Examples 2to 4 was 0.41. *¹Weight parts to 100 weight parts of the resin *²FR-88(trade name, manufactured by FURUKAWA Co., Ltd.) Average particlediameter 0.19 μm *³RLX-A (trade name, manufactured by FURUKAWA Co.,Ltd.) Average particle diameter 3 to 4 μm *⁴UF-007 (trade name,manufactured by Tatsumori Ltd.) Average particle diameter 5 μm

TABLE 2 No. Comparative Comparative Comparative Example 7 Example 8Example 9 example 1 example 2 example 3 First Resin PES*⁰ PES PES PESPES PES layer Inorganic Kind — — — — — — filler Proportion*¹ — — — — — —Second Resin PES PES PES PES PES PES layer Inorganic Kind — — — — — —filler Proportion*¹ — — — — — — Third Resin PES PES PES PES PES Nylon6,6 layer Inorganic Kind Silica*⁵ Calcium Titanium — Titanium — mostfiller carbonate*⁶ oxide*² oxide*² layer) Proportion*¹ 65 65 65 — 120 —Surface-treatment Paraffin fatty acid fatty acid refrigeratingrefrigerating refrigerating wax wax machine oil machine oil machine oilSolvent resistance (xylene) 5H 4H 3H swelled 4H 3H Dielectric breakdownvoltage (kV) 22.6 21.7 26.7 22.0 13.2 20.5 Heat resistance F classpassed passed passed not passed not passed not passed cracked Heat shockresistance good good good poor poor poor cracked cracked High-frequencyV-t property (min) 28.7 19.7 63.9 10.3 0.2 0.4 Static frictioncoefficient 0.10 0.10 0.09 0.15 0.21 0.08 (Note) *⁰reduced viscosity ofPES in Examples 7 to 9 and Comparative example 2 was 0.48, and that inComparative examples 1 and 3 was 0.41 *¹Weight parts to 100 weight partsof the resin *⁵5X (trade name, manufactured by Tatsumori Ltd.) Averageparticle diameter 1.5 μm *⁶Vigot-15 (trade name, manufactured bySHIRAISHI KOGYO KAISHA, LTD.) Average particle diameter 0.15 μm

The multilayer insulated wires of Examples 1 to 9 passed the heatresistance F class, and in the heat shock resistance test, they were notcracked, and the solvent resistance and the chemical resistance weregood.

In Example 1, the insulated wire was one wherein all the insulatinglayers were made of a mixture of a resin and an inorganic fillerspecified in the present invention, the properties including the heatresistance were good, and particularly the high-frequency V-t propertywas excellent.

Examples 2 and 3 were insulated wires wherein two layers including theoutermost layer were made of the above mixture, and the properties weregood and well balanced.

Examples 4 to 9 were insulated wires wherein only the outermost layerwas made of the above mixture, the properties were good and wellbalanced, the dielectric breakdown voltage was high, and thehigh-frequency V-t property was good. The coefficient of static frictionwas small due to the use of a surface-treating agent, and therefore thecoilability was good. In Example 6, since the particle diameter of thesilica was large, the compatibility with the resin was lowered, and thedielectric breakdown voltage and the high-frequency V-t property were alittle low in comparison with those of Example 5. In Example 7, silicahaving a small particle diameter was used, and the insulated wire wasgood in general. Further, in Example 8, since the water-absorptionproperty of the inorganic filler was high, the high-frequency V-tproperty was a little low in comparison with that of Example 5. InExample 9, the conductor was a twisted wire of insulated wires, and thedielectric breakdown voltage and the high-frequency V-t property wereparticularly good.

In contrast, in Comparative Example 1, swelling of the coating wasobserved in the solvent resistance test, and cracks were formed in theheath-shock-resistance test as well as in the heat resistance test.

In Comparative Example 2, since the amount of the inorganic filler wastoo large, the flexibility in the ordinary state was much lowered, andas a result the dielectric breakdown voltage, the heat resistance, andthe heat shock resistance were poor and the high-frequency V-t propertywas conspicuously low.

Comparative Example 3 was an insulated wire whose outermost layer wasmade of polyamide (nylon) 6, 6, the heat resistance was low, the heatshock resistance was poor, and the high-frequency V-t property wasconspicuously low.

INDUSTRIAL APPLICABILITY

The multilayer insulated wire of the present invention is preferablysuitable for use in high-frequency equipments, such as computers, partsof domestic electric equipments, and communication equipments, since itis heat-resistant high enough to satisfy the heat resistance F class, ithas high solvent-resistant, cracks due to heat shock are not formed,and, further, electric properties at high frequencies are good.

Further, the transformer of the present invention wherein the multilayerinsulated wire is utilized, is preferably suitable forelectrical/electronic equipments that are increasingly made small-sized,because the transformer is excellent in electrical properties withoutbeing lowered in electric properties when a high frequency is used in acircuit, and the transformer is less influenced by generation of heat.

Having described our invention as related to the present embodiments, itis our intention that the invention not be limited by any of the detailsof the description, unless otherwise specified, but rather be construedbroadly within its spirit and scope as set out in the accompanyingclaims.

What is claimed is:
 1. A multilayer insulated wire having two or moreextrusion-coating insulating layers provided on a conductor directly orvia some other layer, or provided on the outside of a multicore wirecomposed of conductor cores or insulated cores that are collectedtogether, wherein at least one of the insulating layers is made of amixture prepared by mixing 100 parts by weight of a polyethersulfoneresin that has a reduced viscosity of 0.36 or more, which is theviscosity of 1 g of the polyethersulfone resin in 100 ml ofdimethylformamide measured using an Ubbelohde's viscometer at atemperature of 25° C., and 10 to 100 parts by weight of at least oneinorganic filler selected from the group consisting of titanium oxideand silica; and said layers have an overall thickness within the rangeof 60 to 180 μm.
 2. The multilayer insulated wire as claimed in claim 1,wherein the insulating layer made of the mixture is formed as anoutermost layer or as an outer layer other than the outermost layer. 3.The multilayer insulated wire as claimed in claim 1 wherein theproportion of the inorganic filler in the mixture is increased in anouter layer than an inner layer, successively.
 4. The multilayerinsulated wire as claimed in claim 3, wherein the wire is used in atransformer having a secondary winding provided on a primary winding. 5.The multilayer insulated wire as claimed in claim 1 wherein theinorganic filler has an average particle diameter of 0.1 to 5 μm.
 6. Themultilayer insulated wire as claimed in claim 1, whose surface is coatedwith at least one selected from the group consisting of a paraffin and awax.
 7. A transformer, wherein the multilayer insulated wire in claim 1,is utilized.
 8. The multilayer insulated wire as claimed in claim 1,wherein the insulated wire has heat resistance of class F.
 9. Amultilayer insulated wire having two or more extrusion-coatinginsulating layers provided on a conductor directly or via some otherlayer, or provided on the outside of a multicore wire composed ofconductor cores or insulated cores that are collected together, whereinat least one of the insulating layers is made of a mixture prepared bymixing 100 parts by weight of a polyethersulfone resin that has areduced viscosity of 0.36 or more, which is the viscosity of 1 g of thepolyethersulfone resin in 100 ml of dimethylformamide measured using anUbbelohde's viscometer at a temperature of 25° C., and 20 to 70 parts byweight of at least one inorganic filler selected from the groupconsisting of titanium oxide and silica; and said layers have an overallthickness within the range of 60 to 180 μm.
 10. The multilayer insulatedwire as claimed in claim 9, wherein the proportion of the inorganicfiller is increased in an outer layer than an inner layer, successively.11. The multilayer insulated wire as claimed in claim 9, wherein theinsulating layer made of the mixture is formed as an outermost layer oras an outer layer other than the outermost layer.
 12. The multilayerinsulated wire as claimed in claim 9, wherein the inorganic filler hasan average particle diameter of 0.1 to 5 μm.
 13. The multilayerinsulated wire as claimed in claim 9, whose surface is coated with atleast one selected from the group consisting of a paraffin and a wax.14. A transformer utilizing the multilayer insulated wire of claim 9.15. A multilayer insulated wire having two or more insulating layersprovided on a conductor directly or via some other layer, or provided onthe outside of a multicore wire composed of conductor cores or insulatedcores that are collected together, wherein the insulating layers arecoated by way of extrusion coating, and wherein at least one of theinsulating layers is made of a mixture prepared by mixing 100 parts byweight of a polyethersulfone resin that has a reduced viscosity of 0.36or more, which is the viscosity of 1 g of the polyethersulfone resin in100 ml of dimethylformamide measured using an Ubbelohde's viscometer ata temperature of 25° C., and 10 to 100 parts by weight of at least oneinorganic filler selected from the group consisting of titanium dioxide,silica, alumina, zirconium oxide, barium sulfate, clay and talc: andsaid layers have an overall thickness within the range of 60 to 180 μm.